Retrofit light bulb

ABSTRACT

A retrofit light bulb (1) is disclosed. The retrofit light bulb (1) comprises a substantially flat heat spreader (2) having an opening (5); first and second cover members (7, 8) sandwiching the heat spreader (2), each cover member (7, 8) having a protruding portion (9, 10) directed away from the heat spreader (2) and aligned with the opening (5), the two protruding portion (9, 10) together forming a compartment (11); and one or more solid state lighting devices (18) mounted on a carrier (19) arranged in said compartment (11), in thermal contact with the heat spreader (2), wherein said one or more solid state lighting devices (18) are arranged so that each protruding portion (9, 10) receives light directly from each solid state lighting device (18). The compartment thus forms a single light mixing chamber in which light emitted by all of the SSL devices is mixed.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C.§ 371 of International Application No. PCT/EP2016/054046, filed on Feb.26, 2016, which claims the benefit of European Patent Application No.15156766.6, filed on Feb. 26, 2015. These applications are herebyincorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a retrofit light bulb, more preciselyto a retrofit light bulb having solid state lighting (SSL) devices.

BACKGROUND

WO 2014/087366 A1 discloses a lighting device that comprises a lightemitting portion with at least two solid state light sources. The lightemitting portion includes a first and a second cover member, each havinga light source carrier and a light transmitting portion. The two lightsources carriers are coplanar. The light sources of different lightsource carriers emit light in opposite directions and are equal innumber for a uniform distribution of light around the lighting device.

It is desirable that retrofit light bulbs, such as the one describedabove, be inexpensive to produce and meet high technical performancestandards. Existing retrofit light bulbs can be improved in theserespects.

US 2013/0250587 A1 discloses a LED lamp with a housing formed of a pairof housing members connected to each other in a horizontal direction,that is with a vertical connection line. The LEDs are mounted on acarrier in a horizontal plane, which carrier is kept in position by thehousing members and heat is radiated form the carrier in upwards anddownwards direction.

SUMMARY

It would be advantageous to provide an improved or alternative retrofitlight bulb that is inexpensive to produce and meets high technicalperformance standards.

To better address these concerns, in a first aspect of the inventionthere is presented a retrofit light bulb that comprises a substantiallyflat heat spreader with an opening; first and second cover memberssandwiching the heat spreader, each cover member having a protrudingportion directed away from the heat spreader and aligned with theopening, the two protruding portions together forming a compartment; andone or more SSL devices mounted on a carrier arranged in saidcompartment, in thermal contact with the heat spreader. The one or moreSSL devices are arranged so that each protruding portion receives lightdirectly from each SSL device.

By “substantially flat” is meant that the heat spreader may compriserelatively small portions, such as depressions, protrusions or similar,that depart from the mainly flat shape of the heat spreader. By “inthermal contact” is meant that heat can be transferred from the carrierto the heat spreader through thermal conduction. By a protruding portionreceiving light “directly” from an SSL device is meant that theprotruding portion is the first surface that the emitted light strikesafter leaving the SSL device.

The light bulb described above does not need to have an even number ofSSL devices for the light distribution to be symmetric, something whichmakes it possible to use the lowest number of SSL devices necessary fora particular application. This reduces production costs, the total costof the SSL devices of light bulbs with only a few SSL devices, which arebecoming more and more common, being affected to a particularly largedegree.

Moreover, the compartment forms a single light mixing chamber in whichlight emitted by all of the SSL devices is mixed. Having the light fromall of the SSL devices mix in the same light mixing chamber may reducebinning requirements for the SSL devices (and thus costs). It may alsoenable a particularly efficient mixing of light from SSL devices ofdifferent colors while keeping the total cost of the SSL devices low.

The retrofit light bulb may also have fewer electrical connections thanmany other similar light bulbs. For example, light bulbs having SSLdevices mounted on two sides of a carrier typically require there to beconnections through the carrier which are costly to provide. Light bulbswith several carriers, for example two carriers mounted on a respectiveside of a heat spreader, are another example of light bulbs usuallyrequiring more connections and wires than the retrofit light bulbaccording to the present invention. Fewer electrical connectionstypically means a simpler manufacturing process and lower costsassociated therewith.

According to one embodiment, the opening contains an optical center ofthe retrofit light bulb. The location of the optical center for aparticular type of light bulb is given by industry standards, such asthose of the American National Standard Lighting Group, and positioningthe opening in this way may facilitate compliance with certain industrystandards. Usually, the optical center of a light bulb is located closeto its geometrical center.

According to one embodiment, each protruding portion has a crosssection, which is parallel to the heat spreader and the size of which islarger than or equal to the opening.

According to one embodiment, the first and second cover members havesubstantially the same shape. Such cover members are suitable forapplications requiring a highly symmetric light distribution. It mayalso reduce the numbers of tools needed in the manufacturing process asin some cases the same tools may be used for forming both cover members.

According to one embodiment, each cover member has a flat portion atleast partially surrounding the protruding portion. Such cover memberscan be slim, thereby reducing the size of the retrofit light bulb. Also,heat can be transferred effectively between such cover members and theflat heat spreader because their area of contact may be relativelylarge.

According to one embodiment, the retrofit light bulb comprises amechanical and electrical connector arranged by an end of the retrofitlight bulb. Each SSL device may be arranged to emit light in a directionaway from the connector. The connector can be made to fit in standardlight bulb sockets, making it straightforward to use the retrofit lightbulb in lamps, luminaries, etc., originally intended for traditionalincandescent light bulbs.

According to one embodiment, the protruding portions extend beyond theopening in a direction towards the connector.

According to one embodiment, an end of each protruding portion isprovided with a reflector, the end being distal to the connector. Thereflectors facilitate the meeting of the light distribution requirementsof some technical performance standards, such as “Energy Star”, inparticular when the retrofit light bulb has only a small number of SSLdevices.

According to one embodiment, the retrofit light bulb comprises drivecircuitry arranged on a driver board which is arranged coplanar with theheat spreader, the carrier being mechanically and electrically connectedto the driver board by a connection member. Arranging the driver in thisway can make the light bulb compact and slim.

It is noted that the invention relates to all possible combinations offeatures recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail, withreference to the appended drawings in which:

FIG. 1 shows a schematic exploded view in perspective of an embodimentof a retrofit light bulb; and

FIG. 2 shows a schematic cross sectional view in perspective of theretrofit light bulb in FIG. 1.

As illustrated in the figures, the sizes of layers and regions areexaggerated for illustrative purposes and, thus, are provided toillustrate the general structures of embodiments of the presentinvention.

DETAILED DESCRIPTION

Currently preferred embodiments of the present invention will now bedescribed more fully hereinafter with reference to the accompanyingdrawings. This invention may, however, be embodied in many differentforms and should not be construed as limited to the embodiments setforth herein; rather, these embodiments are provided for thoroughnessand completeness, and fully convey the scope of the invention to theskilled person.

FIGS. 1 and 2 show a retrofit light bulb 1, for example an A21 or A60retrofit light bulb. The retrofit light bulb 1 has an optical axis OAwhich is a central axis of the retrofit light bulb 1. The distributionof light emitted by the retrofit light bulb 1 is approximatelyrotationally symmetric around the optical axis OA. The length l of theretrofit light bulb 1 along the optical axis OA may for example besomewhere between 60 mm and 350 mm. A substantially flat heat spreader 2is arranged along the optical axis OA. The thickness t of the heatspreader 2 depends on the thermal performance required by the intendedapplication, but, typically, the thickness t is in the range from 0.5 mmto 2 mm. The heat spreader 2 can be produced by deep drawing and as asingle piece. Examples of materials which the heat spreader 2 can bemade of include aluminum, aluminum alloys, aluminum oxides, copper,copper alloys, magnesium, zinc, iron, steel, graphite compressed flakes,pyrolytic graphite and thermally conductive plastics with a highgraphite content.

The heat spreader 2 has a first and a second side surface 3, 4 which areflat and parallel to each other. The surface normal of the first sidesurface 3 is perpendicular to the optical axis OA, and the same is truefor the surface normal of the second side surface 4. The heat spreader 2has an opening 5 which is centrally positioned in the first and secondside surfaces 3, 4 and extends therebetween. When viewed along thesurface normal of the first or second side surface 3, 4, the opticalaxis OA splits the opening 5 in two symmetric halves. The opening 5 hasa tapered and curved shape, but other shapes are possible such ascircular and elliptical shapes. The opening 5 contains the opticalcenter of the retrofit light bulb 1, something which may or may not bethe case in other embodiments. A supporting surface 6 is positioned inthe opening 5. The supporting surface 6 is formed in one piece with theheat spreader 2. In other embodiments, the supporting surface 6 may bepart of a piece that has been attached to the heat spreader 2. Thesupporting surface 6 is flat, extends through the opening 5 and projectsoutwards on both sides of the heat spreader 2, thus departing from thesubstantially flat shape of the heat spreader 2. The surface normal ofthe supporting surface 6 is parallel with the optical axis OA. Theoptical axis OA runs through a center point of the supporting surface 6.

The heat spreader 2 is sandwiched between a first cover member 7 and asecond cover member 8, the first cover member 7 facing the first sidesurface 3 and the second cover member 8 facing the second side surface4. The first and second cover members 7, 8 are at least partly made of alight transmissive material. Injection molding can for example be usedfor producing the first and second cover members 7, 8. Examples ofmaterials which the first and second cover members 7, 8 can be made ofinclude PC, PMMA, PET and SAN. The first and second cover members 7, 8have substantially the same shape and are arranged mirror symmetricallywith respect to the plane of the heat spreader 2. The first and secondcover members 7, 8 may be provided with complementary indentations,protrusions, slits, edges, or the like, that allow them to be attachedto each other.

Each cover member 7, 8 is provided with a protruding portion 9, 10directed away from the heat spreader 2. It follows that the protrudingportion 9 of the first cover member 7 and the protruding portion 10 ofthe second cover member 8 are directed in opposite directions. Theprotruding portions 9, 10 have the same shape. The size of the crosssections of the protruding portions 9, 10 is larger than the opening 5,the cross sections being along the optical axis OA and parallel with theheat spreader 2. In other embodiments, the size of the cross sectionsmay be equal to or smaller than the opening 5. The protruding portions9, 10 extend beyond the opening 5 in the direction towards the connector17 (further discussed below). Together, the two protruding portions 9,10 form a compartment 11. The maximum width w of the compartment 11(measured perpendicular to the optical axis OA) differs betweenapplications, the width w depending on, for example, the desired lightdistribution and the number of SSL devices 18 (further described below).In some applications, a suitable value of the width w may be somewherein the range from 5 mm to 50 mm. Any portions of the heat spreader 2that are exposed from the inside the compartment 11 may be covered by areflective material for reasons of optical efficiency.

The protruding portions 9, 10 are provided with a respective reflector12, 23 which may or may not be included in other embodiments. Thereflectors 12, 23 are arranged on the ends of the protruding portions 9,10 that are distal to the connector 17 (further described below). Thelocations of the reflectors 12, 23 are such that light emitted by theSSL devices 18 (further described below) is received by the reflectors12, 23. The reflectors 12, 23 may be formed in one piece with theprotruding portions 9, 10 or attached to the protruding portions 9, 10.The reflectors 12, 23 can be partly light transmissive or configured tobe totally reflective. The reflection of light by the reflectors 12, 23can be specular or diffuse. The reflectors 12, 23 can be made of aplastic material, such as reflective PC, or a metal, such as aluminum.The reflectors 12, 23 may be formed by a coating, for example a whitecoating or a dichroic coating. The reflectors 12, 13 may be formed bytranslucent portions of the protruding portions 9, 10 with high backscattering values.

Each cover member 7, 8 has a flat portion 13, 14 that at least partiallysurrounds the protruding portion 9, 10 of the corresponding cover member7, 8. The flat portions 13, 14 are arranged parallel to the heatspreader 2. The heat spreader 2 and the flat portions 13, 14 are inthermal contact with each other, and this can be achieved in severalways. The flat portions 13, 14 and the heat spreader 2 may for examplebe in direct physical contact with each other, or a thermal interfacematerial may be arranged between the flat portions 13, 14 and the heatspreader 2 so that the flat portions 13, 14 and the heat spreader 2 arein indirect physical contact. Such a thermal interface material may be alayer of glue for attaching the flat portions 13, 14 to the heatspreader 2. Another possibility is that there is an air layer betweenthe flat portions 13, 14 and the heat spreader 2. The thickness of theair layer should be approximately 0.2 mm or less in order for the airlayer not to be thermally insulating.

The first and second cover members 7, 8 have a respective lower portion15, 16. Each of the lower portions 15, 16 is semi circular, and togetherthe lower portions 15, 16 form a tubular neck which is insertable, alonga direction of the optical axis OA, into a mechanical and electricalconnector 17 in the form of a threaded cap. The connector 17 is arrangedby an end of the retrofit light bulb 1 and adapted to be connected to anelectrical socket. The connector 17 can for example be made of a metal,such as aluminum, brass or nickel, or a combination of plastic materialsand metals.

The retrofit light bulb 1 has several SSL devices 18 arranged in thecompartment 11. Other embodiments may have a single SSL device 18. Thenumber of SSL devices 18 can be even or odd. The SSL devices 18 can forexample be semiconductor light emitting diodes, organic light emittingdiodes, polymer light emitting diodes or laser diodes. All of the SSLdevices 18 may be configured to emit light of the same color, forexample white light. Alternatively, different SSL devices 18 may beconfigured to emit light of different colors. The retrofit light bulb 1may for example have red, green and blue SSL devices 18. All of the SSLdevices 18 are arranged to emit light in a direction away from theconnector 17. Both of the protruding portions 9, 10 receive lightdirectly from each SSL device 18. Both protruding portions 9, 10 arethus illuminated by every SSL device 18. The SSL devices 18 are mountedon a carrier 19 extending perpendicular to the heat spreader 2. Thecarrier 19 is flat and has electrical connections for the SSL devices18, the carrier 19 typically being a printed circuit board. In otherembodiments, the carrier 19 may or may not be flat. The carrier 19 maybe arched or V-shaped, for instance. A connection member 20 mechanicallyand electrically connects the carrier 18 to a driver board 21 fordriving the SSL devices 18. The connection member 20 may be formed inone piece with the driver board 21 or formed as a separate part which isattached to the driver board 21. The connection member 20 can forexample be a foil or one or more wires. Drive circuitry 22 is arrangedon the driver board 21. The driver board 21 is arranged coplanar withthe heat sink 2. A portion of the driver board 21 extends into theconnector 17. In other embodiments, the driver board 21 may be arrangedperpendicular to the optical axis OA and/or completely outside of theconnector 17.

The carrier 19 is in thermal contact with the supporting surface 6 andthe heat generated by the SSL devices 18 will be transferred via thesupporting surface 6 to the heat spreader 2, and to the ambient via thefirst and second cover members 7,8.

The retrofit light bulb 1 is put in operation by plugging the connector17 into an electrical socket connected to an electricity supply, wherebythe driver board 21 supplies power to the SSL devices 18 via theconnection member 20 and the carrier 19. The SSL devices 18 emit lightinto the compartment 11 which functions as a light mixing chamber wherethe emitted light mixes before exiting through the first and secondcover members 7, 8. Some of the light emitted by the SSL devices 18strikes the reflective surfaces 12, 13 and is reflected back into thecompartment 11 before exiting. The light leaving through the first andsecond cover members 7, 8 makes up the illumination provided by theretrofit light bulb 1. The heat that is generated during the operationof the retrofit light bulb 1 is transferred to the ambient air via theheat spreader 2 and the first and second cover members 7, 8.

The person skilled in the art realizes that the present invention by nomeans is limited to the preferred embodiments described above. On thecontrary, many modifications and variations are possible within thescope of the appended claims. For example, the connector 17 can beintegrated with the first and second cover members 7, 8. Additionally,variations to the disclosed embodiments can be understood and effectedby the skilled person in practicing the claimed invention, from a studyof the drawings, the disclosure, and the appended claims. In the claims,the word “comprising” does not exclude other elements or steps, and theindefinite article “a” or “an” does not exclude a plurality. The merefact that certain measures are recited in mutually different dependentclaims does not indicate that a combination of these measured cannot beused to advantage.

The invention claimed is:
 1. A retrofit light bulb having an opticalaxis, the retrofit light bulb comprising: a substantially flat heatspreader having an opening, wherein said flat heat spreader is arrangedalong the optical axis and comprises a first side surface and a secondside surface, parallel to each other with a normal perpendicular to theoptical axis; a supporting surface connected to the heat spreader, thesupport surface extending through the opening and protruding through thefirst and second surfaces of the heat spreader; first and second covermembers interposing the heat spreader, each cover member having aprotruding portion directed away from the heat spreader and aligned withthe opening, the two protruding portions together forming a compartment;and one or more solid state lighting devices mounted on a carrierarranged in said compartment, and in thermal contact with the heatspreader through the supporting surface, wherein said one or more solidstate lighting devices are arranged so that each protruding portionreceives light directly from each solid state lighting device.
 2. Theretrofit light bulb according to claim 1, wherein the first cover memberfacing the first side surface, and the second cover member facing thesecond side surface.
 3. The retrofit light bulb according to claim 1,wherein the opening contains an optical center of the retrofit lightbulb.
 4. The retrofit light bulb according to claim 1, wherein saidsupporting surface has normal parallel to the optical axis which runsthrough a center point of the supporting surface.
 5. The retrofit lightbulb according to claim 1, wherein each protruding portion has a crosssection parallel to the heat spreader, the size of the cross sectionbeing larger than or equal to the opening.
 6. The retrofit light bulbaccording to claim 1, wherein the first and second cover members havesubstantially the same shape.
 7. The retrofit light bulb according toclaim 1, wherein each cover member has a flat portion at least partiallysurrounding the protruding portion.
 8. The retrofit light bulb accordingto claim 1, further comprising a mechanical and electrical connectorarranged by an end of the retrofit light bulb, each solid state lightingdevice being arranged to emit light in a direction away from theconnector.
 9. The retrofit light bulb according to claim 8, wherein theprotruding portions extend beyond the opening in a direction towards theconnector.
 10. The retrofit light bulb according to claim 8, wherein anend of each protruding portion is provided with a reflector, the endbeing distal to the connector.
 11. The retrofit light bulb according toclaim 1, further comprising drive circuitry arranged on a driver boardarranged coplanar with the heat spreader, the carrier being mechanicallyand electrically connected to the driver board by a connection member.